The present invention relates generally to processes for producing thermoformed articles, and specifically to such a process wherein the articles are produced using selectively applied differences in temperature.
In conventional thermoforming methodology, a sheet of thermoformable material is heated and indexed to be in registry with a thermoforming apparatus. The apparatus includes a cavity having the "female" portion of the mold, and an insert or "male" portion of the mold, wherein the male and female portions are reciprocally movable relative to each other between a vertically displaced or "resting" position, and a matingly engaged or "forming" position. In the forming position, the heated material is thrust into the cavity by the insert to form the desired shape. Often, vacuum and/or air pressure is used to assist the movement of material in the cavity.
Once the product has been formed in the molding apparatus, the insert is vertically displaced from the cavity, and a vertically displaceable stripper component of the cavity forces the release of the product from the cavity. To provide rapid setting of the formed part, and also to prolong the working life of the thermoforming apparatus, cooling galleries are provided to both the insert and the cavity for controlling operational temperature.
In some cases, the wall thickness of a particular thermoformed part is especially critical, and further, there is a need for providing thermoformed parts having some portions with a first wall thickness, and other portions with a second wall thickness. One such part is a disposable handle for hospital operating room light fixtures, which has a generally circular flange or base portion and a closed tubular handle portion projecting axially from the flange portion.
The flange portion should be fairly rigid for proper mounting to the operating room light fixture. Preferably, the handle portion engages the light fixture with a releasable friction fit and is capable of being secured to the fixture by operating room personnel using only one hand. However, the handle portion should be relatively collapsible for compact shipping. One way of providing such a handle is to produce the disposable handle with the handle portion having a much thinner wall thickness than the flange portion.
However, conventional thermoforming apparatus for molding such disposable handles appears to be incapable of accurately regulating the wall thickness of the handle portion relative to the flange portion. It has been found heated thermoforming material migrates from the flange portion to the tip of the handle portion. This defect increases the amount of thermoforming material needed for each article, and the migrating gives the handle portion a thicker wall which reduces the collapsibility of the handle portion.
One attempted solution to the above-identified problem has been to produce the handle portion separately from the flange portion, and to subsequently join the two components together, such as by ultrasonic welding or chemical adhesive. This procedure solves the problem of migration of material to the handle portion, but is costlier in manufacturing time and effort.
Thus, there is a need for a process for producing thermoformed articles, such as disposable operating room light handle covers, wherein the relative thicknesses of the various components are accurately maintained.
Accordingly, a first object of the present invention is to provide a method for producing thermoformed articles in which a first portion of the article has a first wall thickness, and a second portion of the article has a second wall thickness, the first and second wall thicknesses being substantially different from each other.
Still another object of the present invention is to provide a thermoformed article having first and second portions, each with a corresponding wall thickness, wherein the entire article is integrally formed in a single thermoforming cycle.